There are various applications where it is necessary to pump a relatively small and very precise volume of a fluid which may contain viscous material (i.e. higher viscosity or gooey material). An example of such application is in a medical laboratory where a reagent which contains protein needs to be pumped from a reservoir cup to an analyzer cuvette, generally through a heat exchanger, for performing coagulation analysis. In such applications, the viscous material tends to build up and accumulate on the various parts of the pump which are in contact with the fluid. Such buildup can cause contamination of future samples passed through the pump and can also cause slight alterations in the quantity of fluid being passed through the pump, which variations are unacceptable when measurements to microliter precision are required. However, such materials tend to cling tenaciously to pump parts and are hard to wash off without disassembly of the pump.
One way around this problem is to use peristaltic pumps for pumping such fluids, the fluid in such pumps passing through a tube and not coming in contact with any of the pump parts. The tubing through which the fluid flows is easily removed for cleaning and is generally relatively inexpensive so that contaminated tubing may be replaced where either initial cleaning or further cleaning is not possible, or is not economically feasible.
However, the length of the flexible tube which is operated on by the pump in existing peristaltic pumps cannot be precisely controlled, leading to variations in the volume of the fluid being pumped for each pump revolution. Even if the pump is calibrated for a particular piece of tubing, if that piece of tubing is removed (either for cleaning, to prevent contamination when the pump is used for a different sample or reagent, or for other purposes) the set which the tube inherently takes when in the pump will cause volume variations unless the tube is replaced in exactly the same orientation as the tube had when the calibration was performed. To the extent the tubing has seams, which is the case for many types of tubing used with such pumps, contact of the seams with the operating parts of the pump may also cause slight variations in pumped volume, this being another reason why consistent tube orientation is desirable. However, current peristaltic pumps do not have a facility for assuring such consistent orientation of the tubing.
While the variations in pump volume caused by slight variations in the length of the tubing operated on by the pump are not great, and do not create problems in many applications, such volume variations have made use of peristaltic pumps undesirable in applications where precise pump volumes, accurate to within a few microliters, are required. A need therefore exists for an improved peristaltic pump which is capable of pumping fluids with precision in the microliter range, and in particular which is capable of precisely controlling the length and orientation of the tubing acted upon by the pump so as to facilitate such precision pumping.